Cartilage is a biological tissue which functions by providing a load-bearing, low-friction surface necessary for normal joint operation. The structure of this tissue is composed of a sparse population of cells and a large extracellular matrix (ECM). It is the ECM which allows cartilage to accommodate physiological mechanical loading of the joint. The ECM is composed principally of a hydrated collagen fibril network enmeshed in a gel of highly charged proteoglycan molecules. Proteoglycans are responsible for providing a high fixed charge density which contributes significantly to the overall compressive stiffness of cartilage necessary for normal joint function.
Osteoarthritis is a degenerative joint disease, affecting over 40 million Americans. During motion and weight bearing, osteoarthritis causes significant pain in disease affected individuals. One of the earliest events in osteoarthritis is a molecular level alternation of the cartilage extracellular matrix, and loss of highly charged proteoglycan macromolecules from the matrix. Since the ability of cartilage to withstand compressive loading is due mostly to the presence of proteoglycans, loss of these molecules makes the tissue softer and more susceptible to further wear and degradation. These molecular level changes often occur in very localized regions of cartilage along the joint surface, and occur non-uniformly with depth in the tissue.
The current technologies used for diagnosing such degenerative changes in cartilage matrix, such as x-rays, magnetic resonance imaging and visual inspection by arthroscopy, detect disease at relatively advanced, and probably irreversible, stages. Unfortunately, detection of early degenerative changes, when therapeutic intervention might be most beneficial, is not presently available. Thus, there is a need for the early quantitative assessment of degenerative changes in cartilage.